Acoustic attenuation of engine detonation shock waves



Aprll 14, 1959 A. G. BODINE 2,831,751

ACOUSTIC ATTENUATION OF ENGINE DETONATION SHOCK WAVES Filed Dec. 20, 1957 4 Sheets-Sheet 1 INVENTOR. I ALBERT e. BODINE BY 4 Q I i" I ATTORNEY A ril 14, 1959 Filed Dec. 20 1957 A. G. BODINE ACOUSTIC ATTENUATION OF ENGINE DETONATION SHOCK WAVES Fl G. 2

4 Sheets-Sheet 2 INVENTOR.

ALBERT G. BODI NE ATTORNEY April 14, 1959 A. G. BODINE ACOUSTIC ATTENUATION OF ENGINE DETONATION SHOCK WAVES Fil ed Dec. 20, 1957 4 Sheets-Sheet 5 FIG. 3

INVENTOR.

ALBERT G. BODINE BY 1 I- ATTORNEY April 14, 1959 A. G. BODINE 2,881,751 1 ACOUSTIC ATTENUATION OF ENGINE DETONATION SHOCK WAVES 'Filed Dec. 20, 1957 4 Sheets-Sheet 4 INVENTOR ALBERT G. BODINE BY f.

ATTORNEY United States Patent ACOUSTIC ATTENUATION OF ENGINE DETONATION SHOCK WAVES Albert G. Bodine, Sherman Oaks, Calif. Application December 20, 1957, Serial No. 704,033 16 Claims. (Cl. 123-191) This invention relates generally to the art of acoustic attenuation along the transmission paths radiating from the source of the manifestations of detonation or combustion roughness in internal combustion engines.

In my prior Patent No. 2,573,536, as well as in a number of subsequent patents, I have disclosed the principle of acoustic suppression of detonation in both piston and continuous combustion or jet engines. These patents have disclosed a number of specific means or devices for combatting detonation, whether in carburetor engines, manifold injection engines, or cylinder injection engines, including diesels. Reference to the aforementioned patent is made for a full disclosure of the principle of acoustic detonation suppression and various techniques for applying the same. In connection with that fundamental teaching, it must be recognized that this invention is not concerned with suppression of the detonation phenomena.

I have noticed in my experimental work with various applications of acoustic detonation suppression that the repeated cycle engine, such as the piston engine, has the significant characteristic that the combustion cycle is repeated in successive totally independent cycles. Thus there is repeated the initiation of various transient phenomena, to a much greater extent than is the case with the continuous combustion family of engines. In the latter the fuel and air mixture is ignited when the engine is started, and combustion is maintained more or less constant, with the only qualification that the combustion becomes undesirably undulatory, thus requiring acoustic treatment.

In the case of piston engines, however, the ignition and subsequent fuel combustion steps are necessarily a series of separated or discretely repeated events. I have noted that with some engines the phenomena of detonation frequently involves an initial transient of shock nature. Referring again to my above-mentioned Patent No. 2,573,536, and particularly to Figure 8a thereof, there is shown at A the initial shock which very often precedes detonation phenomena. As has been explained, there are variations of this condition wherein the initial shock is the cycle of greatest amplitude, and the repeated cycles thereafter are of gradually decaying amplitude.

As set forth in said patent, I have found that acoustic wave suppression means incorporated in connection with the combustion chamber of an engine will greatly reduce the mean eifective amplitude of the overall acoustic phenomena. The result is that the overall energy represented by the acoustic phenomena is very greatly reduced. This energy factor is of primary importance to engine durability. Accordingly, from the pure engineering standpoint, it is true that totally satisfactory results in all respects can be accomplished by acoustic suppression of the repeated wave phenomena within the combustion chamber. However, there is still an important factor, which may be thought of more as a matter of personal psychology than a matter of satisfactory engine operation and durability, associated with the initial shock type spike involved insome forms of detonation. In this connection, it is to be recalled that the initial shock or spike here spoken of, which is a transient condition that initiates the detonation cycle, is not necessarily or always removed by the detonation suppression means and methods disclosed in my aforementioned patents. Instead, this initial shock may initiate the process, and the process is then immediately suppressed or snufied out.

The initial shock or spike which thus may remain even during the practice of acoustic detonation suppression may be noticeably audible even though its energy content is for all practical purposes nil. It can be somewhat disturbing to sensitive people, especially under conditions of otherwise very low background noise from other sources. Thus, to illustrate further, while the acoustic suppression of detonation waves within the combustion chamber is in most cases adequate to meet all requirements, there still remain a few isolated special situations, typified by an acoustically treated luxury passenger car climbing a long difiicult mountain in the quiet countryside. Here the least tinkle owing to detonation can still be detected by the discriminating person, notwithstanding use of acoustic detonation suppression practices. By the term detonation I intend to include the whole family of combustion vibration or combustion roughness phenomena.

Accordingly, it is the primary object of this invention to reduce the transmission of the particular kind of sound Waves spoken of above from the combustion gases through the mechanical wall structure of the engine, whereby to eliminate radiation of detonation sound at audible levels.

It is an object of this invention to reduce the detonation shock frequency acoustic transmission properties of the combustion chamber walls, water jacket body, water jacket walls, pistons, and other associated mechanical structure. That is to say it is an object of the invention to reduce the acoustic Q of the engine structure outside the combustion chamber for detonation shock frequencies. The invention is illustratively carried into effect by any combination of techniques and devices to be presently set forth. These are all to be distinguished from such acoustic wave suppression devices as are disclosed in my aforementioned patent and others related thereto, in that the latter devices are in gaseous or immediate sound wave communication with the combustion chamber of the engine. They react on the acoustic wave processes inside the combustion chamber. The sound wave attenuating devices of the present invention, are, by contrast, in a wave transmission path in the engine structure located outside the chamber. They are removed from immediate acoustically coupled relations with the combustion chamber, and do not react on or have any attenuative effect on the acoustic wave phenomena existing within the combustion chamber. Acoustic attenuator pockets or elements in the combustion chamber walls, in communication With the combustion chamber, are to be distinguished from the present invention in this respect.

Practice of the invention may involve reduction of the flexural vibration of engine walls, and/ or the reduction of longitudinal transmission of waves through the engine wall structure, by reduction of the acoustic Q of the metal itself, or its structural form.

One preferred practice of the invention is to reduce the acoustic Q of the engine structure for detonation frequencies by applying a coating of viscous material on surfaces of the structural parts that tend to transmit detonation noise. I may, for example, apply such a layer of viscous material on the wall surfaces of the water jacket space. This can be accomplished by pouring into the jacket ports a material such as molten tar, or other viscous material which has been made temporarily fluid by combination with a volatile solvent. After the material sets up, there results a thick coating of viscous material on the internal water jacket surface;

'frequency content of the initiating shock phenomena above described. A further important improvement resides in applying a relatively stiff or rigidly setting coating'material over the layer of viscous material. This Qadded stiff coating over the underlying viscous layer greatly enhances the acoustic damping of the sound wave within the viscous material. In particular, the effect is to damp shear phenomena within the viscous substance. It-Will be seen that this form of my invention, i.e., a layer 'of viscous material, preferably with an additional layer of a stiff substance coated thereover, may be applied to any-vibrating wall surface, and in fact, this particular acoustic wave attenuator means has a wider application than to the limited field of acoustic engine treatment. Used inside the water jacket of the engine, however, this practice of the broad invention is particularly easily ap- "plied and particularly useful.

57 A further practice of the invention is to provide discontinuities in the sound wave transmission through the engine structure, which discontinuities function either as a substantial change in acoustic reactance, at detonation "frequencies, so as to cause the wave energy to be reflected back toward the combustion chamber, or to be present in an attenuative wave path which gradually and progressively absorbs the wave. A further practice of the invention is the use of loose or unattached inertia bodies in contact with wave transmitting wall surfaces, such as undergo or cause out-ofphase reflections at detonation frequencies and resulting damping of the wave.

Various other objects, features and variational forms of the invention will appear and be described in the course of the following detailed description of a number of illustrative embodiments thereof, reference for this purpose being bad to the accompanying drawings in which:

Figure 1 is a vertical sectional view through an engine incorporating acoustic attenuating means in accordance with the invention; Figure 1a is a fragmentary view showing a modification of a portion of Figure l;

Figure 2 is a view similar to Figure 1 but showing a modified species of the invention;

, Figure 2a is a detailed section taken on line 2a--2a 'of Figure 2;

Figure 2b is a view similar to Figure 2a but showing a modification; and,

Figures 3, 4 and 5 are transverse vertical sections of engines showing further modified forms of the invention.

In Figure 1 is shown a valve-in-engine, equipped with certain'acoustic detonation wave suppression means in accordance with the invention disclosed by my Patent No. 2,573,536, and equipped also with illustrative forms of "shock wave attenuator means in accordance with the present'invention. The engine is shown to have a watercooled block 10, water-cooled head 11 fastened to block 10, and piston 12 reciprocable in cylinder 13 in block 10. Head 11 comprises a generally domed combustion chamber'wall 14 defining a combustion chamber 15. Block and head 11 have coolant jackets 10a and 11a, respectively. In the center of head wall 14 is a threaded port to receive spark plug 17. Intake and exhaust valves open to combustionchamber 15 through wall 14, an exhaust valve being indicated at 18, and the intake valve, not shown, being understood to be located forwardly of the plane of the drawing.

Formed in the generally hemispheric wall 14 of engine head 11 are threaded ports 19 and 20 to receive acoustic detonation attenuators 21 and 22, respectively. These attenuators 21 and 22 may be of the nature shown in Figure 21 of my Patent No. 2,573,536, and a detailed disclosure thereof will not be necessary herein.

Figure 1 shows also, as a further means for suppressing detonation sound waves within the combustion chamber, a porous pad 23 is mounted on the top end of the piston 12. Also, the top of the piston, beneath the pad 23, is shown as formed with resonant absorber cavities 24, also as described in my aforementioned patent.

The attenuator devices so far described in connection with Figure 1 will be understood to operate in communication with the combustion chamber to attenuate the full acoustic wave pattern associated with detonation, with the exception of the initial shock or spike with which the detonation pattern is initiated, and various means in accordance with the invention for preventing transmission through the combustion chamber walls of a sound wave resulting from the initial detonation shock wave or spike will next be set forth.

The interior surfaces of water jacket 10a and head jacket 11a have applied thereto a relatively thick layer of a viscous acoustic damping material. Such a layer is shown at 30 in jackets 10a and 11a. It can be applied by pouring a temporarily fluid, but essentially viscous material, into the water jacket space and then tipping the part about until the surfaces are adequately coated. For example, a material such as molten tar, or a viscous material made temporarily fluid by combination with a volatile solvent, is poured into the jacket ports. When the material thus coated onto the interior surfaces has set up, a thick coating of the viscous material adheres to the internal jacket surfaces. Such a coating of viscous material is eifective to absorb and attenuate sound waves otherwise transmitted through the wall structure of the engine, it being noted, however, that a material should be used which, in combination with the particular elastic stiffness of the wall structure, has an energy absorbing frequency response for the particular frequency content of the shock wave phenomena desired to be subdued. The section of an appropriate material in any given case is within the skill of those versed in the acoustics art.

A further improvement, as shown in the left half of Figure 1, consists in applying over the thick viscous layer 30, a second or outside layer 31 of a stifi or rigidly setting coating material. Such a material, an example of which is a phenolic varnish, may be introduced and applied over the initial layer 30 after the latter has set up. This still outside layer greatly increases the acoustic shear wave damping phenomena within the underlying viscous material.

In Figure 2 I have shown a valve-in-head type engine having a water-cooled block 40, water-cooled head 41 secured thereto, and piston 42 reciprocable in cylinder 43. A spark plug 44 is mounted in head 41, and intake and exhaust valves are shown at 45 and 46, respectively. Combustion chamber 47 defined by head wall 48 is provided over cylinder 43. The intake and exhaust valves control fluid mixture intake and exhaust gas passages 50 and 51 opening into the combustion chamber.

The valves are shown provided with suitable guides and valve actuating mechanism, not necessary to describe herein.

The two valves 45 and 46 may be provided with acoustic detonation suppressing attenuators of the type shown in Figure 26 of my aforesaid Patent No. 2,573,536, and the engine may be provided with any other detonation suppression means, as desired.

The water jacket cavity of head 41 is indicated generally by numeral 52, and in accordance with the practice of the invention under consideration, this cavity is filled with or contains a multiplicity of loose bodies, such as balls 53. These separate bodies or balls, which may be typically of approximately marble size, may be composed of any suitable material such as steel, glass, ceramic or plastic. Ordinary glass marbles can serve the purpose very well. These separate bodies provide free passage ofthe water jacket fluid through the spaces therebetween.

The dissipation of the acoustic, shock-type spike with which an acoustic detonation wave is generally initiated may be considered under two heads. Notwithstanding the acoustic suppression of the wave pattern following the initial spike by practices taught in my Patent No. 2,573,536, this spike or peaked half-wave, starts a vibration of the combustion chamber wall 48, and one mode of attacking the problem consists in heavily damping this wall vibration. Second, the half-wave spike itself may be attacked directly by methods or means designed to disperse it through random multiple reflections. The particular action applied or realized in any given case depends largely on the type of ball or other body 53 that is used.

Assume first the use of heavy balls, roughly of marble size, composed, e.g., of steel or iron. The acoustic damping action of these balls arises from their being in contact with the water jacket side of the combustion chamber Wall. Acoustic flexural modes of vibration of this wall are opposed by the loose balls in engagement therewith, and the wall is thereby heavily damped. The balls are caused to vibrate in out-of-phase relation to the combustion chamber wall and to one another, because of acoustic impedance mismatch at detonation frequencies throughout the entire combination of flexural wall, ball mass, and intervening water. There results a very attenuative condition, acoustic energy being absorbed by friction between the moving balls and the combustion chamber wall, and between one another, by non-linear impacts, which tend to convert basic frequency to random frequencies, by internal friction within the balls, and by acoustic wave dispersion owing to random reflections from the surfaces of the balls. The damping will be seen to be cumulative through the mass of loose bodies.

"As stated above, steel, iron, or other heavy metallic balls exert a heavy damping action on the combustion chamber walls, and thereby greatly reduce transmission of detonation sound from the combustion chamber through the engine structure.

The halls may alternately be composed of non-metallic materials, such as glass, ceramic, or plastics, which offer less mass reaction, but which consume more acoustic energy internally by internal damping.

It is in' all cases important that the bodies in contact with the combustion chamber wall and with each other must meet the structural requirement of having an attenuative frequency response for the detonation frequencies to be combatted, particularly the frequency content of the shock phenomena above described.

In a modification of the invention, the bodies used in the water jacket may be hollow plastic balls, made like Ping Pong balls, and can be smaller, e.g., of common marble size. A group of such balls 55 is shown in Figure 2b, and it will be understood that these may be installed in the water jacket of the engine, as in Figures 2 and 24. These hollow or gas-filled balls greatly enhance sound wave dispersion by reason of great impedance mismatch at the boundaries between the balls and the combustion chamber wall and at the boundaries between the balls and the surrounding water. The sound waves radiated by the combustion chamber wall, upon encountering such balls, are partially transmitted and partially reflected at each wall-to-ball interface, at each water-toball interface, and at each interior Wall surface-to-gas interface. These reflections rapidly degrade and disperse the sound wave, and transmission entirely through the mass of balls is comparatively slight. Any remaining transmission is of a much lower order than the transmission that can otherwise take place through water in the'water jacket.

In Figure 3 is shown an engine embodying another form of the invention. At 65 is shown an L-head watercooled block, to which is fastened water-cooled head 66, block 65 having cylinder 67 in which works a piston 68.

An exhaust valve is indicated at 69, and a spark plug at 70. It will be understood that, as in conventional L- head engines, an intake valve (not shown) will be located alongside exhaust valve 69, such valve being, of course, out of the plane of the drawing. Block 65 and head 66 have coolant jackets 71 and 72, respectively, and head 66 has a combustion chamber space 74 over the cylinder and valves, as indicated. The water jacket 72 is divided into compartments or passages 75 by vertical webs 76, the compartments 75 being understood to be interconnected around or behind said webs; and the webs 76 are here shown as breached by a substantial number of acoustic spoiler cavities, here in the nature of pipe resonators consisting of straight cylindrical bores 77 opening inside the combustion chamber. Such spoiler cavities and their function in suppressing the detonation Wave is fully set forth in my said Patent No. 2,573,536, and need not be repeated herein.

The several combustion chamber wall portions 73 intervening between the water jacket compartments and the combustion chamber are contacted, within the water jacket compartments, by metal bridge plates such as 80a, 80b, 80c and 80d. These plates 80a-80d are designed to contact the adjacent wall surfaces at spaced points, as shown, and to introduce a frictional sliding action at such points. The spacing distance is determined with references to the wave length for the lateral wave existing in or being transmitted through the adjacent combustion chamber wall as a result of the detonation phenomena, as earlier explained. Thus, the combustion chamber wall portions 73, as a consequence of detonation shock are set into a flexural, lateral vibration of characteristic frequency. Such vibration often occurs in definite acoustic patterns, with spaced nodal and antinodal regions. The antinodal regions are of course those at which vibration amplitude is maximized and the nodal regions are those at which vibration amplitude is minimized. Accordingly, the plates 8011-8012 are preferably designed with such spacing between contact points as will assure that the antinodal regions will not all be bridged. In other words, the plates 80a-80d should each contact one or more velocity antinodal regions. This is assured if the wave frequency of interest is ascertained, the corresponding wave length in the combustion chamber wall is then found, and the spacing distance between contact points on the plates 80a-80d is then made such as will assure at least one antinodal region being contacted. Clearly, as one example, a one-quarter wave length spacing of the contact areas on the plates will assure some degree of contact with the vibrating antinodal regions of the walls. It is also important that the spacing distances between contact points not be very much smaller than a quarter wave length, since in such case, frictional sliding action is materially reduced.

The metal plates Still-80a are preferably held against the adjacent combustion chamber wall surfaces by spring pressure. In the case of plate 80a, the plate itself is somewhat resilient, and is so bent as to engage not only the bottom but the sides of the corresponding coolant compartment. It is resilently deformed upon installation, and is thereafter spring actuated to engage the wall surfaces opposite.

' Plates 80b, 80c, and 80d are provided with coil compression springs 84 holding them against the adjacent wall surfaces. In the case of plates 80c and 80d, the corresponding springs 84 are also provided at the top with additional plates 85, engaging the underside of the top wall of the water jacket.

Thus, flexural vibration of the combustion chamber engine wall 73 results in a friction action with the springpressed metal plate, which friction action is dissipative of detonation sound wave vibration otherwise transmitted through that portion of the engine structure. This frictional dissipation of acoustic energy can be further increased by .introducing alayer-Stld' of a viscous material, such: as between the plate 80d and the wall, 73. j Figure 3 shows alsoa further modification of conventional engine structure giving an acoustic attenuation property in accordance with the invention. In general,

tionship to the combustion chamber wall. These webs can be cut through and still maintained in contact at -.the cut, with the result that. compressional loading can still be carried, but any vibration being transmitted through the webs is greatly damped if the cut is oriented properly in relation to the sound waves. The webs 76 in Figure 3 are shown with such cuts at 90, 91, and 92. Acoustic damping eifect at such a cut results largely from out-of-phase reflections of the wave caused by the discontinuity in the wave transmission path. In addition, the cut can introduce a dissipative resistive impedance at detonation frequencies, especially if an acoustic shear material is embodied or introduced into the cut. For example, the cut 92 at the top of the right hand web 76 in Figure 3 shows an introduced layer I 93 of thermo plastic material. It will be seen that longitudinal (vertical) vibrations in the walls 76 are reflected by the cuts or discontinuities 9G, 91, and 92 oriented at right angles to the direction of transmission of these vibrations, while lateral or fiexural vibrations in-the walls 76 are dissipated by friction between opposed sliding surfaces at the cuts 90, 91, and 92, or by shear friction of a substance introduced into a cut, as at 93.

, Figure 4 shows an engine generally similar to that of- Figure 3, again made up of a block indicated at 100, and a water-cooled head 101, block 100 having a cylinder 102 for piston 103, and head 101 providing an L- head type combustion chamber head wall generally indicated at 104. The combustion chamber head wall is in this case made up in two parts, an elevated part 104a forming an integral portion of the head casting, and a laminated portion 104!) overlying a major portion of the cylinder bore immediately at the top end of the latter. These laminations may be integrated to one anotherby welding at the periphery thereof, and the welded lamination assembly may then be welded in place to the head casting as indicated in Figure 4. Such a laminated wall construction has a substantial acoustic attenuative property for high frequency transmission and, in accordance with the invention, is designed in accordance with known principles to have an acoustic attenuative frequency response for the detonation frequency content desired to be suppressed. The stock type detonation wave pulse is greatly attenuated by such a laminated wall structure, and transmission through the engine structure to the outside is correspondingly reduced.

In Figure 5, I have shown a further modification of the engine made up of cylinder block 110, cylinder head 112, and piston 113 working in cylinder 114 in cylinder block 110. The piston is again shown with a porous pad 115 mounted on its top, designated for detonation wave suppression, and below this pad 115 there may be spoiler cavities similar to those shown in the piston structure of Figure 1. These features of the engine were disclosed in my aforesaid Patent No. 2,573,536 and need not be further described herein.

Head 112 is formed with water circulation passages 116 and 117, and mounts, at the top, a spark plug 118.

The head 112 is formed to provide a domed combustion chamber head wall 119. In this particular instance, the

purpose is, essentially, reduction of the wave transmission property of the structure of cylinder head 112 at the frequencies involyedin the, detonation shock phenomtics, the purpose .is to reduce the acoustic Q of the head structure, whereby acoustic detonation: wave transmission therethrough will be materially reduced.- To this end, the structure of cylinder head '112- is made somewhat cellular or interrupted as regards wave lengths of the order of the transmitted frequencies .tobe combatted. is illustratively accomplished by-machining holes or pockets such as indicated at .120 int'gthe wall of the cylinder head. Additionally, or alternatively, a plurality of foreign bodies of material such as indicated at 121 are'included in the metal of thehead, thereby introducing acoustic discontinuities within" the metal structure, whereby the acoustic Q of the .metal itself is greatly reduced. For example, these foreign materials or bodies may consist of non-alloying inclusions for dispersions introduced into the iron in the molten. states, such as higher melting point metals, or ceramics. These bodies introduce substantial variances in acoustic impedance at random locations throughout the-head'structure, and therefore cause random reflections which are highly dispersive of the detonation frequency sound waves attempting to pass through the head structure. Flexural vibration of flat surfaces of the engine are particularly well subdued by this method of reducing the acoustic Q of the metal. The discontinuities or foreign-introduced bodies should, of course, be such as will effect an attenuative frequency response at those frequencies-involved-in the shock phenomena .to be combatted. r

One further variant of my invention involves the. introduction of a frequency responsive attenuation elementsin an attachment means between two components of the engine. For example, as illustrated in Figure 1,-I maynuse a form of piston wherein the piston crown part 130. is separate from the piston body part 131, and is acoustically isolated at detonation frequencies from the body portion and the mechanical structure therebeyond. Asshown, the crown has an internal cylindrical surface 132, which is frictionally engaged by an externalannular rib 133 "on the piston body, the crown having a friction, press fit over the rib 133. In the pocket between rib 133 and" the shoulder 134 above, on the crown 130, is fitteda ring 135 of low Q, vibration absorbing material, such'as fiber glass, plastic, or tetrafluorethane. A shoulder underlying the rib 133, afforded by a clamp ring 136 secured to the bottom of crown 30 as by rivet pin 137, holdsa second ring 138 of vibration absorbing material against the lower side of rib 133. In engine operation, the piston is acted on by the body of burning combustion gases functioning as a compliance, and assuming a proper mass for the piston crown, the crown will tend to vibrate during detonation. The crown accordingly vibrates relative to the piston body, sliding slightly up and down on the body, and acoustic energy is dissipated at the frictional junction between crown and body, as well as within the vibration absorbing rings '135 and 138. By making the mass of the body portion of the piston proper in relation tothe compliance of the connecting rod, the body will also have a frequency response, and increased relative frictional vibration between crown and skirt can be attained.

In Figure 1a I have shown a modification, wherein the piston crown 140 and piston body 141 are separated by a plastic insert ring 142. This insert, which may be a thermosetting phenolic, introduces a viscous shear effect between the two components of the piston. The introduced material should have an attenuative frequency response characteristic for the detonation wave frequencies whose transmission is to be reduced. I

I have now shown and described a number of practices of my present invention. Briefly summarizing, the invention introduces an attenuative characteristic into the engine structure, such that shock or other acoustic wave phenomena arising from detonation, and not suppressed 9 through the engine structure to outside. The various attenuative devices here shown may be used in various combinations in various portions of the engine structure to assure against escape of material audible sound from detonation. The invention is preferably practiced in combination with my techniques for suppressing the detonation wave pattern inside the combustion chamber. However, my inventions may also be practiced without detonation wave pattern suppression within the combustion chamber, and while in such case the engine is not relieved from the physical shock of detonation, audible manifestations are nevertheless made less disagreeable. It will also be understood that while various forms of the invention have been disclosed herein, numerous other forms are evidently possible, and these are to be considered as coming within the scope of the broader of the appended claims.

I claim:

1. In an internal combustion engine having a combus tion chamber wherein detonation may occur, engine walls including wall means defining said combustion chamber and including wall structure whose solid material forms an acoustic Wave transmission path leading outwards from said chamber, said wall structure being physically vibratory as a consequence of wave transmission therein owing to detonation within said chamber, and thereby acting as an acoustic radiator, and acoustic attenuating means acoustically coupled into said physically vibratory wall structure in said wave transmission path outside the defining wall surfaces of the combustion chamber, said attenuating means having an attenuative response for the frequency pattern of the accoustic wave transmitted through the solid material of said wall structure from the detonation phenomena within the combustion chamber.

2. The subject matter of claim 1 wherein said acoustic attenuating means comprises a layer of viscous material on at least a portion of said wall structure in said wave transmission path.

3. The subject matter of claim 1 wherein said acoustic attenuating means comprises a layer of viscous material on at least a portion of said wall structure in said wave transmission path, and a layer of relatively stiff material over said layer of viscous material.

4. The subject matter of claim 1 wherein said acoustic attenuating means comprises a layer of viscous material on interior water jacket surfaces of the engine.

5. The subject matter of claim 1 wherein said acoustic attenuating means comprises a layer of viscous material on interior water jacket surfaces of the engine, and a layer of relatively stifi material over said layer of viscous material.

6. The subject matter of claim 1, wherein said acoustic attenuating means comprises a mass of loose bodies positioned in contact with one another and with at least a portion of said wall structure in said wave transmission path.

7. The subject matter of claim 6, wherein said bodies possess substantial inertia whereby to effect a substantial damping of said wall structure against wave transmission therethrough.

8. The subject matter of claim 6, wherein said bodies have substantial internal damping.

9. The subject matter of claim 6, wherein said bodies are ball shaped.

10. The subject matter of claim 6, wherein said bodies are hollow and composed of light material.

11. The subject matter of claim 6, wherein said bodies are spherical, hollow, and composed of light material.

12. The subject matter of claim 6, wherein said engine has a water jacket defined in part by an exterior surface of a combustion chamber wall, and said mass of loose bodies is contained within said jacket, in contact with said exterior surface of said combustion chamber wall.

13. The subject matter of claim 1, wherein said engine wall structure has a wall surface bounding said acoustic wave transmission path, and said acoustic attenuating means includes a plate spring-urged into engagement with said wall surface.

14. The subject matter of claim 1, wherein said engine wall structure has a wall surface bounding said acoustic wave transmission path, and said acoustic attenuating means includes a bridge plate spring-urged in engagement with said wall surface at a plurality of points spaced by a substantial fraction of a detonation shock frequency wave length distance in said wall structure adjacent said bounding wall surface.

15. The subject matter of claim 1, wherein said acous tic attenuating means comprises a multiplicity of nonalloying foreign particles incorporated in the vibratory wall structure in such dispersion and of such material as to introduce substantial variances in acoustic impedance in said wave transmission path and thereby cause random wave reflections and dispersion of acoustic detonation frequency waves attempting to follow said path.

16. In the operation of internal combustion engines, the method of reducing audible detonation induced acoustic wave frequencies initiated in the combustion chamber of the engine, transmitted through the surrounding wall structure of the engine, and radiated from the outer surface of said structure, that comprises attenuating said wave frequencies in course of their transmission through said wall structure of the engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,752,907 Bodine July 3, 1956 

